The present invention relates to a device for converting into analog form a digital information signal constituted by binary numbers representative of the sine and cosine trigonometric components by a variable angle, and to the display in analog form, particularly by the rotation of a needle on a dial, of this angular information provided by a digital computer. This is a conventional problem in the aeronautical equipment industry, the computer is question being an air navigation computer of the type employed on board an aircraft.
Two solutions of this type of problem are presently known, depending on whether the digital information to be converted is of angular or trigonometric nature.
When the information is angular, the conversion is made either by using a servo-controlled coder in which the angular position is determined by the cancellation of the error signal supplied by a digital comparator, or by using a servo-controlled potentiometer in which the angular position is determined by reproducing the analog signal obtained after decoding of the digital information.
When the information is trigonometric, two of the binary numbers are decoded and converted into positive or negative D.C. voltages of amplitudes respectively equal to the sine and cosine values of the angle. These voltages are then memorized to be finally used to supply a resolver of potentiometric or, preferably, electromagnetic nature. In the latter case, it is necessary to modulate the two D.C. voltages to obtain two A.C. voltages, having an amplitude ratio equal to that of the two D.C. voltages, and having relative phases which are representative of the signs of the sine and cosine. These A.C voltages are then applied to the two stator windings of the resolver, which may be provided with a compensation winding, so that the voltage induced on the rotor of the resolver, after amplification, controls a servomotor. The servomotor orients the rotor until the voltage induced on the rotor is cancelled, thus determining, upon stoppage of the motor, an angular position (relative to a predetermined starting position) on the axis of the rotor, thereby representing the angle which it is desired to display.
Insofar as it is desired to obtain an acceptable degree of accuracy and reliability in carrying out decoding, memorising and modulation operations, considerable production difficulties are encountered, from the technological standpoint, which have repercussions on the weight and cost of the device.